·1925年4月25日兴登堡当选德国总统
·1926年4月25日礼萨-汗自立为波斯国王
·1936年4月25日中国共产党提议建立抗日人民阵线
·1945年4月25日盟军与苏军在德国易北河会师
·1945年4月25日联合国制宪会议开幕
·1950年4月25日时装大师迪奥举行他的首次时装展览
·1953年4月25日科学家指出脱氧核糖核酸是双螺旋结构
·1963年4月25日国防部授誉“南京路上好八连”
·1967年4月25日西德之父阿登纳逝世
·1971年4月25日孟加拉国建立
·1976年4月25日社会主义者苏亚雷斯出任葡萄牙总理
·1982年4月25日以色列撤走在西奈的最后一批士兵
·1989年4月25日日本首相竹下登因贿赂案丑闻辞职
·1990年4月25日西德总理候选人拉方丹遇刺
·1996年4月25日张学良移居夏威夷
·1996年4月25日日本奥姆真理教教主麻原彰幌受审
·1997年4月25日中国递交《禁止化学武器公约》批准书
·1998年4月25日香港新国际机场竣工
1953年4月25日
科学家指出脱氧核糖核酸是双螺旋结构
1953年4月25日，在《自然》杂志上发表的一篇文章中，詹姆斯-沃森博士和
弗朗西斯-克里克博士提出提出了脱氧核糖核酸(DNA)的新结构。脱氧核糖核酸是
遗传的基本分子结构。这篇文章否定了林纳斯-泡令的观点。泡令认为脱氧核糖核
酸是a(阿尔法)螺旋。沃森和克里克提出这种遗传物质是双螺旋结构模式，即由互
补化学碱基对组成的两条螺旋绕链。这使人们能够想象基因是如何复制并携带信
息的。
1953 DNA replication
Watson and Crick's double-helical model of DNA suggested a mechanism for the replication of DNA.
In their April 1953 DNA structure paper, Watson and Crick noted: "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material."
A month later, in their second paper, they published their hypothesis for the replication of DNA:
"…If the actual order of the bases on one of the pairs of chains were given, one could write down the exact order of the bases on the other one, because of the specific pairing. Thus one chain is, as it were, the complement of the other, and it is this feature which suggests how the deoxyribonucleic acid molecule might duplicate itself.
Watson and Crick, ‘The molecular structure of the gene’ (1953). Pages from a draft of the second Watson and Crick paper, ‘Genetical implications of the structure of deoxyribonucleic acid’, Nature 1953 171: 964-7.
Previous discussions of self-duplication have usually involved the concept of a template, or mould. Either the template was supposed the copy itself directly or it was to produce a 'negative', which in its turn was to act as a template and produce the original 'positive' once again. In no case has it been explained in detail how it would do this in terms of atoms and molecules.
Now our model for deoxyribonucleic acid is, in effect, a pair of templates, each of which is complementary to the other. We imagine that prior to duplication the hydrogen bonds are broken, and the two chains unwind and separate. Each chain then acts as a template for the formation onto itself of a new companion chain, so that eventually we shall have two pairs of chains, where we only had one before. Moreover, the sequence of the pairs of bases will have been duplicated exactly."
This mechanism - termed semiconservative replication - was confirmed experimentally in 1958 by Matthew Meselson and Franklin Stahl.
"Why, then, did we change our minds and, within only a few weeks, write the more speculative paper of May 30? The main reason was that when we sent the first draft of our initial paper to King's College we had not yet seen the papers by the researchers there.
Consequently we had little idea of how strongly their X-ray evidence supported our structure. Jim had seen the famous 'helical' X-ray picture of the B form reproduced by Franklin and Gosling in their paper, but he certainly had not remembered enough details to construct the arguments about Bessel functions and distances that the experimentalists gave. I myself at that time had not seen the picture at all. Consequently we were mildly surprised to discover that they had got so far and delighted to see how well their evidence supported our idea. Thus emboldened, Jim was easily persuaded that we should write a second paper." |
